Secondary batteries called lithium ion batteries, currently attracting attention. They can broadly be classified into two categories of so called lithium ION secondary batteries and lithium METAL secondary batteries. The lithium METAL secondary batteries utilize precipitation and dissolution of lithium for the operation. Besides, the lithium ION secondary batteries utilize storage and release of lithium in the charge-discharge reaction. These batteries both can realize charge-discharge at large energy densities as compared with lead batteries or nickel-cadmium batteries. By making use of this characteristic, in recent years, these batteries have been widely applied to portable electronic equipment such as camera-integrated VTR's (video tape recorders), mobile telephones, and notebook computers. In accordance with a further expansion of applications, the development of lightweight secondary batteries such as to allow higher energy densities has been advanced as a power source of the portable electronic equipment. Furthermore, there is a strong demand for size reduction, service life prolongation, and safety enhancement.
Regarding a liquid electrolyte, a particular combination of materials has widely been employed, for non-aqueous secondary batteries as represented by lithium ion secondary batteries or lithium metal secondary batteries (hereinafter, these may be collectively referred to simply as a lithium ion secondary battery), in order to realize high electric conductivity and potential stability. That is, a carbonic acid ester-based solvent such as propylene carbonate or diethyl carbonate is employed, in combination with an electrolyte salt such as lithium hexafluorophosphate.
With respect to the composition of a liquid electrolyte, a technique for making various kinds of additives to be contained in a liquid electrolyte is proposed for the purpose of improving battery characteristics. For example, Patent Literature 1 describes an attempt to improve coulombic efficiency and the like of a lithium electrode of lithium metal batteries by adding a predetermined aromatic compound. Patent Literature 2 discloses an example such that various organic compounds are applied as an overcharge preventing agent in a secondary battery using lithium titanate for a negative electrode. Further, Patent Literature 3 describes an attempt to improve cycling characteristics by using aromatic compound additives having specific solvents and specific structures.